Tailoring the AD7173-8 ADC input range

I would like to take full advantage of the ADC's input range while using the internal buffers.

I have configured the ADC to run from a single +3.3V supply.

If the internal buffers are turned on, the absolute analog input range become 0 to 2.2V.

If I use a 1.1V external reference, the ADC range will match the absolute analog input range.

I don't think I want to use a resistor divider off of the ADR441 to create a 1.1V reference.

Should I buffer this signal with an amplifier for the reference?

- James

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  • 0
    •  Analog Employees 
    on Aug 19, 2015 12:07 AM

    Hi James,

        The ADR441 has a voltage noise of 1.2uVp-p and a 48nv/rtHz of voltage noise density. The AD7173-8 has an available internal buffer for the internal reference. Using a resistor divider to have a 1.1V to ADC Ref pin maybe suitable, since the output impedance of the ADR441 is zero or almost zero ( please refer to fig. 31 of the ADR441 datasheet) at lower frequencies and considering the effect of resistor thermal noise could be very minimal ( you may find the formula in the web) and enabling the buffer in the AD7173-8 at the same time to have a High input impedance on the buffer, this will have 1.1V on the Reference of the ADC.

          There is a 0.44 attenuation amplifier available with ADI like AD8475 have a  2.5uVp-p output voltage noise.

          I'll try to check on the people here from our amplifiers group if they can recommend. Do you have some specifications that need to be consider other than that was mentioned before?

    Regards,

    Jonathan

Reply
  • 0
    •  Analog Employees 
    on Aug 19, 2015 12:07 AM

    Hi James,

        The ADR441 has a voltage noise of 1.2uVp-p and a 48nv/rtHz of voltage noise density. The AD7173-8 has an available internal buffer for the internal reference. Using a resistor divider to have a 1.1V to ADC Ref pin maybe suitable, since the output impedance of the ADR441 is zero or almost zero ( please refer to fig. 31 of the ADR441 datasheet) at lower frequencies and considering the effect of resistor thermal noise could be very minimal ( you may find the formula in the web) and enabling the buffer in the AD7173-8 at the same time to have a High input impedance on the buffer, this will have 1.1V on the Reference of the ADC.

          There is a 0.44 attenuation amplifier available with ADI like AD8475 have a  2.5uVp-p output voltage noise.

          I'll try to check on the people here from our amplifiers group if they can recommend. Do you have some specifications that need to be consider other than that was mentioned before?

    Regards,

    Jonathan

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